The present invention relates to a scanning device for use with a veneer lathe and, more particularly, to such a device including one or more ultrasonic transducers for providing an indication of the diameter of a peeler block or log mounted on the spindle of the lathe.
In the lumber industry, wood veneer is produced utilizing a veneer lathe. A log or "peeler block" of appropriate length is clamped in the rotatable spindle of the veneer lathe and presented to a veneer peeling knife which extends along the entire length of the block. The log is initially rounded up on the lathe into a peeler block of uniform radius. Thereafter, the spindle is rotated and the knife is moved radially inward to peel a continuous layer of veneer from the outside of the block, continuing along a spiralling path toward the block center. The peeling operation is completed when only a small cylindrical core of wood is left.
It is desirable to monitor the amount of wood supplied to the lathe and to keep an accurate record of both the amount of veneer and the amount of scrap produced. Specifically, it is desirable to be able to record the gross log diameter, the diameter of the peeler block after it has been rounded up into a cylindrical shape on the lathe, and the diameter of the core which is left after the peeling operation is completed.
Prior art systems for making such measurements have generally been limited to optical scanning of a log prior to loading it onto the veneer lathe. Such optical scanning systems are relatively complicated and typically are subject to error. Additionally, they may also be limited in the resolution obtainable. Systems such as shown in U.S. Pat. No. 3,806,253, issued Apr. 23, 1974, to Denton, as shown in U.S. Pat. No. 4,139,035, issued Feb. 13, 1979, to Bystedt, or as shown in U.S. Pat. No. 4,152,767, issued May 1, 1979, to Laliotis, in which the log image is focussed onto an array of photosensitive transducers, such as photodiodes, may be limited in accuracy in that the measurement is actually based upon converging light rays which are tangential to the log surface generally on opposite sides of the log, but not at points directly opposed along a log diameter.
Another type of optical scanning device is shown in U.S. Pat. No. 3,746,065, issued July 17, 1973, to Mason, in which the log is transported through a scanning area in a direction perpendicular to the axis of the log. A row of light sources and an opposing row of sensors on opposite sides of the scanning area extend generally perpendicular to the direction of log movement. The log is thereafter rotated by 90.degree. and transported again through the scanning area. While providing greater accuracy, the Mason system requires a substantial amount of equipment and the requirement of passing the log through the scanning area twice limits the log scanning speed.
U.S. Pat. No. 3,513,321, issued May 19, 1970, to Sherman, discloses a log tally system in which the log is transported through a scanning station in a direction parallel to the axis of the log with a row of light sources and an opposing row of light sensors being provided on opposite sides of the scanning station. Each of the rows is arranged generally perpendicularly with respect to the direction of log movement. In this system, the resolution of measurement is limited by the spacing between adjacent sensors.
Another type of optical scanning system is disclosed in U.S. Pat. Nos. 3,852,579, issued Dec. 3, 1974, to Sohn et al., and 3,992,615, issued Nov. 16, 1976, to Bennett et al. In this system, the log is mounted on a rotatable spindle of a charger mechanism and rotated thereon for determining the radius of the log at a number of angularly displaced points around the log periphery. The measurement is accomplished by directing a narrow beam of modulated light to strike the surface of the log. Light reflected from the log is received and focussed upon a photodetector for demodulation. The distance to the log surface from the light source is determined by measuring the relative phase of the modulating and detected signals. This system, however, is relatively complicated.
Accordingly, it is seen that there is a need for a simple, accurate log scanning system for scanning a log mounted on a veneer lathe, to monitor the radius of the log or peeler block prior to, during, and after peeling.